I'm a relative newbie, but... Since you're on Windows, what's the possibility of taking the opposite approach, & making the thumb drive ALWAYS be the same letter. Then just assigning C:\strawberry\etc... to the X: or Q: or whatever you've mapped it to?
Comment on Re: Changing Perl compile-time configuration settings
My assumption is that group policies etc. have been properly secured (except for the use of flash drives, doh!) and you can't do squat machine wise. You get the drive you're given.
I also want to be able to take this thing to meetings/interviews jam it in the Windows presentation machine and my scripts to work.